Method and apparatus for selectively activated powered actuation of a hydraulic drive system

ABSTRACT

A method and apparatus for selectively activating a gravity down mode of a hydraulic system during operation of a lift gate. An electronic control circuit is added to hydraulic control circuitry and is configured to selectively interrupt the power down mode or gravity down mode of operation of the hydraulic system based on either a manual input (override) or a sensed condition and switch to the other mode of operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 13/529,058 filed on Jun. 21, 2012, which is a Divisional ofU.S. patent application Ser. No. 12/392,204 filed on Feb. 25, 2009, nowU.S. Pat. No. 8,234,046.

BACKGROUND

1. Field of Technology

The present invention relates to hydraulic systems. More particularly,it relates to the selective activation of a powered mode and/or agravity mode for lowering a lift gate.

2. Discussion of Related Art

In a typical configuration, many hydraulic lift gate systems operate ina gravity down mode. “Gravity down” means that the force of gravitydrives the lift gate from one position to another. For example, the liftgate platform may be driven by the force of gravity from a first upperposition to a second lower position. The present disclosure, however, isnot limited to this particular example. Any change in configuration oflift gate components that is driven by gravity, e.g., movement of theplatform from a folded to an unfolded configuration, is considered agravity down mode for the purposes of the present disclosure.

The gravity down mode consumes the least amount of energy as the weightof the gate lowers the platform to the ground. With light platformsand/or in cold weather, however, there can be problems with the platformlowering to the ground or traveling to the ground too slowly. Also, asthe hydraulic oil becomes more viscous in cold temperatures, it willmove more slowly through the system in the gravity down mode. Thiscreates a problem for truck fleets operating in seasonal climates, asthe fleet operator may have to incur the expense of changing the oil inthe hydraulic lift system to a different viscosity depending on theseason.

A conventional solution for customers with this issue is to purchase, ata higher price, a hydraulic liftgate system that applies hydraulic powerboth to raise and lower the platform. The use of hydraulic power tolower a platform is referred to as a “power down”. The disadvantage ofthis alternate system is that the customer will not enjoy the benefitsof energy savings of operating in a gravity down mode when power down isnot necessary.

Other customers that do not operate in cold weather, may still benefitfrom a power down mode in certain circumstances. For example, the loadon the platform increases the speed at which the lift gate platformlowers and a power down mode may not be needed depending on the weightof the load. However, when lowering an empty platform, particularly analuminum or other lightweight construction platform, the driver may wanta power down mode to speed up the lowering of the platform to save time.

As noted above, the power down system requires more components andconsumes more energy, thereby using more battery power. Experience hastaught that some customers can have an issue with the batteries runningout of power before finishing their route. Thus, conserving batterypower is an important issue, particularly for fleet operators with manystops and short routes. Accordingly, a system is needed that providesthe option of a power down mode of operation when needed, but which alsoenables the conservation of battery power when it is determined that itis not needed.

SUMMARY

The present principles relate to structures for selecting between a“powered down” mode and a “gravity down” mode for actuating a hydrauliclift gate system, such as that used on delivery trucks. Moreparticularly, the present principles relate to allowing for an automaticor manual activation of a power down mode for actuating a hydraulic liftgate system in conditions when non-powered, gravity driven movementproduces substandard or otherwise undesirable performance.

According to an implementation, the hydraulic lift gate system includesan electronic control circuit configured to enable the selectiveactivation of a power down mode of operation of the hydraulic lift gatesystem during the gravity down mode of operation of the lift gate.

According to another implementation, the method for controlling ahydraulic lift gate system includes sensing a condition during thegravity down mode of operation requiring a switch to power down mode ofoperation, and activating the power down mode of operation by switchingfrom gravity down mode to power down mode upon a determination of thepresence of the sensed condition.

The method further includes sensing at least one condition such as, forexample, hydraulic fluid flow, fluid pressure, ambient temperature,fluid temperature and/or battery condition, determining whether thesensed at least one condition meets a predetermined threshold level, andgenerating a control signal when the sensed condition meets thepredetermined threshold level, said control signal functioning toactivate the power down mode.

According to yet another implementation, the method for controlling ahydraulic lift gate system includes sensing a condition during the powerdown operation requiring a switch to gravity down mode of operation, andactivating the gravity down mode of operation by switching from powerdown mode to gravity down mode upon a determination of the presence ofthe sensed condition. The sensed condition may be, for example,hydraulic fluid flow, fluid pressure, ambient temperature and fluidtemperature. Once a condition is sensed, it is determined whether thesensed condition meets a predetermined threshold level, and when itdoes, a control signal is generated to activate the gravity down mode.

Other aspects and features of the present principles will becomeapparent from the following detailed description considered inconjunction with the accompanying drawings. It is to be understood,however, that the drawings are designed solely for purposes ofillustration and not as a definition of the limits of the presentprinciples, for which reference should be made to the appended claims.It should be further understood that the drawings are not necessarilydrawn to scale and that, unless otherwise indicated, they are merelyintended to conceptually illustrate the structures and proceduresdescribed herein.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings wherein like reference numerals denote similar elementsthroughout the views:

FIG. 1 is a single pump hydraulic schematic diagram of an exemplaryhydraulic system;

FIG. 2 a is a partial electrical schematic diagram of the pump boxelectronic control of a hydraulic system according to known systems;

FIG. 2 b is a modified electrical schematic of the electronic control ofthe hydraulic system according to an implementation of the presentprinciples;

FIG. 2 c is an exemplary schematic of the electronic control circuitimplementing a delay circuit according to an implementation of thepresent principles;

FIG. 2 d is a modified electrical schematic of the electronic control ofthe hydraulic system according to an implementation of the presentprinciples;

FIG. 3 is an exemplary working diagram of the power unit and valveoperation during gravity down mode of the hydraulic system according toan implementation of the present principles;

FIG. 4 is an exemplary working diagram of the power unit and valveoperation during power down mode of the hydraulic system according to animplementation of the present principles;

FIG. 5 is an exemplary schematic diagram of a hydraulic system includingtwo hydraulic pumps;

FIG. 6 a is an electrical schematic diagram of the electronic control ofa two pump hydraulic pump system according to known systems;

FIG. 6 b is a modified electrical schematic diagram of the electroniccontrol of the two hydraulic pumps in the system shown in FIG. 6according to an implementation of the present principles;

FIG. 7 is a flow chart of the method for entering power down modeaccording to an implementation of the present principles; and

FIG. 8 is a flow chart of the method for entering gravity down modeaccording to an implementation of the present principles.

DETAILED DESCRIPTION

According to one implementation disclosed herein, the gravity down modeis set and then, when desired, the operator can activate a switch to runthe gate in a power down mode. For example, in the case of trucksoperating in cold or winter type weather, the operator may use the powerdown mode more often. In addition, if there is a load on the platformthe power down mode will generally not be needed, but when the platformis empty the operator may want to activate the power down mode to speedup the lowering of the lift gate and save time.

A liftgate with a selectively activated (powered) lowering system isprovided for lowering of the liftgate platform. According to animplementation, the system has two modes: 1) gravity down; and 2) powerdown. Gravity down may be used as desired to simply let gravity lowerthe platform.

Referring to FIG. 1 there is shown a hydraulic drive system 10 having amotor 12, a pump 18 and a plurality of solenoid valves (e.g., valve A,valve B, valve C, valve E and valve H) which control the flow (anddirection) of hydraulic fluid through the various ports A, J, B, C andE. The ports are designated as follows: port A is for the closing line;port J is for the power open line; port B is for the lifting line; portC is for the power down line; and port E is a filter.

By way of example, the system 10 may have a cylinder 16 and at least oneleft and right cylinder 14L and 14R, respectively. Cylinder 16opens/closes the gate, and cylinders 14L and 14R raise/lower the gate.Although shown in a particular configuration, those of skill in the artwill recognize that cylinders 14L and 14R could be reversed to provide apull/push operation rather than a push/pull operation, without departingfrom the scope of the present invention. Generally, an electrical systemprovides power to a motor and thereby a pump that forces fluid, e.g.oil, from a reservoir through a valve into a cavity of the cylinderwithin which a piston is disposed. When the piston begins in a firstretracted position, the positive pressure exerted by the fluid on thebutt end of the piston forces it out toward a second extended position.Conversely, when a piston is in an extended position, positive pressureexerted by fluid can force it into a retracted position. The piston inturn may be attached to another component that one desires to move inconcert with the movement of the piston. For 14L and 14R: if the valveis closed, the piston will remain in its retracted position provided noother outlet is provided for oil exiting the cylinder. When one desiresto extend the piston, one can open an outlet valve D, which allows oilto be forced out of the cavity of the cylinder by the weight of thepiston and any load bearing on the piston. One of ordinary skill in theart will recognize that the viscosity of the oil, the temperature of theoil, total load on the piston and oil flow controls will be among thefactors determining how fast the piston moves to an extended position.

According to one aspect of the present principles, a switch is providedthat allows the operator to selectively activate a power down mode. Theswitch may be of a manual, electronic or solid state configuration. Inthe power down mode, a pump provides pressure to the upper cavity of thecylinder, which urges the oil into the cylinder at a faster rate thanthe pressure exerted by the piston alone. This switch may be used when,for example, the operator decides that the rate of the piston'sextension is undesirably slow during gravity down mode.

Referring to FIG. 2 a, there is shown an electrical schematic of thecontrol electronics 20 a for the single pump hydraulic system shown inFIG. 1. As shown, a battery 22 is connected to the solenoid switch 26via a master disconnect switch 24. Those of skill in the art ofhydraulic systems will recognize the construction and operation of thesingle pump system depicted in FIGS. 1 and 2 a, and understand that thepresent invention may be applied to multi-pump systems without departingfrom the scope of the same. By way of further example, a dual pumpsystem can be configured where both pumps operated during the power downon demand of the present invention. Alternatively, in anotherconfiguration of a dual pump system, one pump can be used for gravitydown and one for power down. Those of skill in the art will recognizethat a switch or automatic sensor can be used to switch between pumps ina dual pump system without departing from the scope of the presentinvention.

FIG. 2 b shows an electrical schematic diagram of the controlelectronics 20 b according to an implementation of the presentprinciples. As shown, gravity/power down control circuit 30 has beenadded to the schematic. The gravity/power down control circuit 30includes a relay 32 and a two (2) position switch 34. The relay 32 hasbeen added to the electrical connection (i.e., line 101) between the Fconnection on the receptacle and the control input of the solenoidswitch 26. The solenoid switch 26 controls the activation/deactivationof the motor 12 and thereby pump 18 depending on the position of switch34. The two (2) position switch 34 has a gravity down mode connector 36connected to control input of the relay 32, a common (or neutral)connector 37 connected to the E port on the connection receptacle, and apower down mode connector 38 connected to one of the two connectors ofsolenoid valve C. FIG. 2 c shows another embodiment of the electroniccontrol circuit 30 implementing a time delay 40 described in more detailbelow.

The operation of gravity/power down system of the present invention willnow be described with reference to FIGS. 2 b, 3 and 4. When the switch34 is in gravity down mode (Position 2), it disconnects the wire 102from the C solenoid valve and connects the wire 102 from the B solenoidvalve to relay 32 coil input.

Because the motor starter solenoid switch activation wire 101 is on thenormally closed contact of the relay 32, every time the B solenoid valvereceives electrical power it turns on the relay 32 and disconnects thewire 101 from the starter solenoid switch 26.

When the switch 34 is moved into the power down position (Position 1),then the B solenoid valve is connected to the C solenoid valve throughthe switch 34, and the relay 32 will not be energized. With thisconnection on power down function, the wire 101, which is connected tothe normally closed contact of the relay 32, will energize the startersolenoid switch 26, which will turn on the motor 12, and because the Csolenoid valve is energized it will change the direction of thehydraulic fluid flow (i.e., through port C) and thereby provides thedesired powered lowering of the lift.

FIGS. 5 and 6 a shows an example of a dual pump hydraulic system 50 andcorresponding electrical schematic 60 a for controlling the same. Aselector switch 62 is provided to allow selection between motor 1 ormotor 2, depending on the desired operation.

FIG. 6 b shows a modified electrical schematic 60 b where thegravity/power down control circuit 30 has been added to the circuit. Forgravity down mode, both B solenoid valves are open (i.e., on both of thetwo hydraulic systems) and the fluid flows back to the reservoir easierthan when one valve is open and as a result, the lift platform will movedown faster.

When the switch 34 is moved to the power down position then, the “B”solenoid valve will be connected to the “C” solenoid valve via theswitch 34, and relay 32 will not be energized when the “B” solenoidvalve is energized. With this connection on the power down function;wire 64, which is connected to the normally closed contact of relay 34,will energize the starter solenoid 26 which will turn on the motor 12,and because the “C” solenoid valve is energized it will change thedirection of the oil flow and will create the desired power downscenario.

According to another aspect of the present principles, one or moresensors (e.g., a system of sensors) may be provided to trigger the powerdown mode automatically during gravity down mode, depending on variousfactors, or a combination thereof. Examples of such factors can be thespeed of the platform, the weight of the platform and load, thetemperature and/or pressure, fluid flow, the battery condition, etc.

FIG. 2 d shows various possible sensor or manual inputs to theelectronic control circuit 30 according to an exemplary implementation.Those of skill in the art will recognize that circuit 30 may includefurther circuitry or control logic 42 replacing switch 34 fortranslating received sensor signals or manual input into a switchingcontrol signal depending on the desired application and/orimplementation. The control logic can be any suitable circuitry workingin conjunction with the sensors to provide the desired selectiveactivation (i.e., manual or automatic) of the powered down mode ofoperation of the lift.

By way of further example, a speed sensor can be used to detect thespeed of movement of the piston or platform in order to provide acontrol signal to activate the power down mode when the speed dropsbelow a predetermined level. The speed sensor could be located, forexample, in the cylinder and on the gate and could operate in any knownmanner (e.g., radar). Yet another example, a pressure sensor system mayprovide a control signal to activate the power down mode when thepressure in the cylinder speed drops below a predetermined level (e.g.,pressure sensor could be located in the flow line after the flow controlor anywhere in the flow line. In a further exemplary implementation, atemperature sensor system may provide a control signal to activate thepower down mode when the temperature (ambient or in the cylinder) dropsbelow a predetermined level. By way of example, if the temperature fallsbelow 50° F., depending on the climate and/or particular use, the powerdown mode would be activated.

The temperature sensors could be disposed in multiple locations, forexample, outside near the gate, but in one preferred implementation thetemperature sensor can be located in the oil in the pump reservoir andcylinders. Those of skill in the art will appreciate that the placementof the temperature sensors will be a matter of design choice and can beanywhere in the system without departing from the scope of the presentinvention. Similarly, the control logic 42 could receive a switch inputfrom a geographic positioning system (GPS) or geographic positioningsensor which can identify the lift location, measure the speed of thevehicle and based on predetermined criteria for specific geographicareas, the operation of the lift can be controlled. For example, if theGPS unit says the lift is operating in Nebraska, the system can:automatically change to the power down mode in winter months; reducemaintenance cycles to bring the lift in for service more often; and makea note to maintenance to use a thinner oil for the cold weatherenvironment.

In yet another exemplary implementation, a battery condition sensorwould sense how fast the battery voltage level drops when a load isadded, and how fast the voltage recovers once the load is removed. Inthe event of a battery condition that is undesirable, the power downmode could be prevented and the lift would stay in the gravity down modeof operation.

Those of skill in the art will recognize that the types of sensors usedand the positions of the same may vary without departing from theintended scope of the present principles.

FIG. 7 shows a method 70 according to an implementation of the presentinvention. Initially, gravity down mode is started (either manually orby default). According to an implementation of the present invention,the gravity down mode can be entered upon start up of the system or atany time after an initially entered powered down mode. Once in gravitydown mode, the possible conditions for entering the power down mode arethen monitored 74 via the one or more sensors described above. Adetermination 76 is then made as to whether the threshold for arespective sensor has been met. When the threshold condition has beenmet, power down mode is entered 78. When the threshold condition is notmet, the monitoring or sensing 74 of the conditions for entering powerdown mode is continued.

According to one implementation, the sensed condition 74 could be amanual override 75 by an operator. In this instance, the system willbypass all sensor threshold determinations and proceed directly toentering power down mode 78.

FIG. 8 shows a method 80 according to an implementation of the presentinvention. Initially, power down mode is started (either manually or bydefault). According to an implementation of the present invention, thepower down mode can be entered upon start up of the system or at anytime after an initially entered gravity down mode. Once in power downmode, the possible conditions for entering the gravity down mode arethen monitored 84 via the one or more sensors described above. Adetermination 86 is then made as to whether the threshold for arespective sensor has been met. When the threshold condition has beenmet, gravity down mode is entered 88. When the threshold condition isnot met, the monitoring or sensing 84 of the conditions for enteringpower down mode is continued.

According to one implementation, the sensed condition 84 could be amanual override 85 by an operator. In this instance, the system willbypass all sensor threshold determinations and proceed directly toentering power down mode 88.

In accordance with another implementation, the control electronics forthe hydraulic system lift gate can be programmed to delay the start upof the pump/motor upon initial activation of the lift gate. This delayis preferably in a range of 1 ms-500 ms, but may have a longer range of1 ms-5 seconds, for example, depending on the desired need and/orapplication. Those of skill in the art will appreciate that the delaymay be considerably longer or shorter, and still be consistent with theintended scope of the invention.

This delay is useful in allowing the solenoids that need to actuate atthe same time as the motor/pump to be at a full operating voltage whenthe pump motor kicks on. Those of skill in the art will recognize thatwhen the pump motor turns on, the voltage in the system can drop acrossthe solenoids, in which case the solenoids cannot activate as intended.When the solenoids do not have a proper operating voltage (i.e., theapplied voltage is too low), the solenoid cannot actuate and can causeproblems in the proper operation of the gate. FIG. 2 c shows anexemplary implementation of the electronic control circuit 30 having atime delay circuit 40 coupled to one output leg of the relay 32.

Since the pump motor drags down the voltage such that the solenoidscannot operate simultaneously with the activation of the pump motor, theimplementation of a slight delay at the start of the pump/motor, willenable the solenoids will to reach an appropriate operating voltagewhich is high enough to activate them. Once activated, the solenoids canhold in their operating position at the lower voltage after pump motoractivation.

While there have been shown, described and pointed out fundamental novelfeatures of the present principles, it will be understood that variousomissions, substitutions and changes in the form and details of themethods described and devices illustrated, and in their operation, maybe made by those skilled in the art without departing from the scope ofthe same. For example, it is expressly intended that all combinations ofthose elements and/or method steps which perform substantially the samefunction in substantially the same way to achieve the same results arewithin the scope of the present principles. Moreover, it should berecognized that structures and/or elements and/or method steps shownand/or described in connection with any disclosed form or implementationof the present principles may be incorporated in any other disclosed,described or suggested form or implementation as a general matter ofdesign choice. It is the intention, therefore, to be limited only asindicated by the scope of the claims appended hereto.

What is claimed is:
 1. A hydraulic lift gate system for a hydraulic liftgate attached to a vehicle, the system comprising: an electronic controlcircuit integrated into the system and being configured to enableactivation of a gravity down mode of operation of the hydraulic liftgate attached to the vehicle at any time during a power down mode ofoperation, said activation of gravity down mode of operation isperformed in response to a sensed condition that occurs during the powerdown mode of operation.
 2. The hydraulic lift gate system according toclaim 1, wherein the electronic control circuit comprises: a twoposition switch having a gravity down mode and a power down mode.
 3. Thehydraulic list gate system according to claim 2, wherein the electroniccontrol circuit comprises: a relay having a control input and twoconnectors connected inline to a control line of the hydraulic system;and wherein the two position switch includes a gravity down connectorconnected to the control input of the relay and a power down connectorconnected to a power down line within the hydraulic system and a centralconnector connected to a hydraulic control connection receptacle.
 4. Thehydraulic lift gate system according to claim 1, further comprising atleast one sensor for monitoring a condition of the hydraulic lift gateand generating a control signal for the electronic control circuit inresponse to the monitored condition.
 5. The hydraulic lift gate systemaccording to claim 4, wherein the monitored condition comprises at leastone selected from a group consisting of geographic location of the liftgate system, hydraulic fluid flow, fluid pressure, ambient temperature,fluid temperature, battery condition and speed of lift.
 6. The hydrauliclift gate system according to claim 1, wherein the electronic controlcircuit further comprises a delay circuit configured to delay startingof a hydraulic pump/motor for a predetermined time period uponactivation of the power down mode.
 7. The hydraulic lift gate systemaccording to claim 3, wherein the electronic control circuit furthercomprises control logic configured to receive an input and generate acontrol signal in response to the received input.
 8. The hydraulic liftgate system of claim 5, wherein said monitored condition furthercomprises a determination whether the monitored condition meets thepredetermined threshold level, wherein when the monitored conditionmeets the predetermined threshold level, said control signal functionsto activate the gravity down mode.